Well, I'm not JB, but since no one else is saying anything ...
I've always found light rifles tend to be sensitive to the way they are held. More so than a heavy varmint rig anyway. Apart from watching the obvious stuff, like making sure swivels aren't dragging on the rest, I've found that holding them firmly tends to help, rather than letting them free-recoil. I also am careful to ensure the buttplate is on the shoulder (actually, just inboard of the shoulder, on the muscle) in the same position, and with the same pressure each time(fairly firm). I hold the fore-end in my weak hand, with it in turn resting on the front rest, and pay attention to the same things I would do if shooting prone, like making sure the trigger finger doesn't touch the stock, consistent head position and elbow position, and positioning myself for a natural point of aim on the aiming mark to avoid "muscling" the rifle.
This is not standard benchrest technique, I know, but it works much better for me. I have several rifles which weigh less than 7 lbs scoped, but will consistently put 5 rounds into less than 1 moa shot this way, some less than .75 moa. As well, the POI better matches the POI I get from typical field positions.
HTH
